We estimate income underreporting by the self-employed in Switzerland and compare our results with existing international estimates. For better comparability, we use a methodology developed by Pissarides and Weber (1989), which has been widely applied in the international community. We also discuss factors that might affect underreporting estimates derived with this method. We find evidence for income underreporting by the self-employed in Switzerland. However, compared to other countries, our figures are relatively low. Furthermore, we do not find statistically significant differences in underreporting between language regions or cantons with different tax burdens.